This study presents the development of the Basic Manobo Expression Dictionary: A Mobile-Based Application, designed to aid in the preservation, promotion, and accessibility of the Manobo language, one of the indigenous tongues in Agusan del Sur. With the increasing risk of language extinction brought about by modernization, younger generations are less fluent in traditional dialects. To address this issue, the researchers designed and developed a mobile-based dictionary application that provides users with translations of commonly used Manobo expressions into Filipino and English. The study employed the Systems Development Life Cycle (SDLC) methodology, integrating features such as categorized vocabulary, audio pronunciation guides, and user-friendly navigation. The system was evaluated by students, teachers, and selected community members using the ISO 25010 quality model. Findings showed strong acceptability across all criteria, with the highest scores in Usability (4.72) and Functional Suitability (4.68), confirming that the application is both practical and effective. The overall weighted mean of 4.65 indicates that the system successfully meets its objectives. Results demonstrate that the mobile dictionary can significantly contribute to cultural preservation, language education, and technology-driven heritage conservation.